Kondo Effect in the Presence of Itinerant-Electron Ferromagnetism Studied with the Numerical Renormalization Group Method

Abstract

The Kondo effect in quantum dots (QDs)-artificial magnetic impurities-attached to ferromagnetic leads is studied with the numerical renormalization group method. It is shown that the QD level is spin split due to the presence of ferromagnetic electrodes, leading to a suppression of the Kondo effect. We find that the Kondo effect can be restored by compensating this splitting with a magnetic field. Although the resulting Kondo resonance then has an unusual spin asymmetry with a reduced Kondo temperature, the ground state is still a locally screened state, describable by Fermi liquid theory and a generalized Friedel sum rule, and transport at zero temperature is spin independent.

Nonequilibrium spin-current detection with a single Kondo impurity

“…36 A spin-dependent hybridization for the spin-up and spin-down energy levels of the impurity is then predicted, resulting in an effective static magnetic field at the impurity site (this field can eventually be compensated by an external magnetic field). 29,31,35 In the presence of ferromagnetism, the Kondo resonance therefore splits apart as confirmed experimentally. 32,37 While such a splitting is well understood, the impact of a nonequilibrium spin current on the Kondo resonance has so far been little addressed in correlated nanostructures.…”

“…[12][13][14][15][16] It has also been successfully evidenced in nanoscale devices, [17][18][19][20][21] in particular quantum dots, [17][18][19][22][23][24] carbon nanotubes, [25][26][27] and nanowires. 28 Of particular interest-especially in the context of spintronics, is the issue of screening in the presence of a magnetic environment such as spin-polarized electrodes [29][30][31][32][33][34][35] and spinpolarized edge states. 36 A spin-dependent hybridization for the spin-up and spin-down energy levels of the impurity is then predicted, resulting in an effective static magnetic field at the impurity site (this field can eventually be compensated by an external magnetic field).…”

Interference effects on Kondo-assisted transport through double quantum dots

“…The spinpolarization of the leads gives rise to the difference in the DOS between up-and down-spin conduction electrons, so that the resonance width Γ α m,nσ should be spin-dependent. To represent how large the strength of the spin polarization is, we introduce the effective spinpolarization strength p, following the definition given in the literature [37,38,39,40,41,42,43,44,45,46,47,53,54]:…”

“…We also discuss the DQD systems with ferromagnetic (FM) leads. This is stimulated by the recent extensive study of spin-dependent transport through a QD coupled to FM leads in the context of spintronics [37,38,39,40,41,42,43,44,45,46,47,48]. Since the Kondo effect is sensitive to the internal spin degrees of freedom, notable phenomena caused by the FM leads are expected to appear in transport properties.…”

Nonequilibrium transport theory of the singlet-triplet transition: Perturbative approach

“…These devices are promising candidates for our future electronics, and might possibly be used as building blocks of spintronics devices and spin-based quantum computers, too. 8 Moreover, the unprecedented control of these minuscule structures opens new and fascinating possibilities to build and study hybrid structures, [9][10][11][12][13] entangle electron spins, 14 and also to realize and study simple quantum systems in the close vicinity of quantum phase transitions under non-equlibrium conditions. [15][16][17][18][19] Understanding the physical properties of these tiny electronic circuits represents a major challenge to theoretical as well as to experimental physicists.…”